1. Field
The following description relates to a technique for optical transmission in an optical transport network, and more particularly, to a transmission technique for serial and parallel channel interworking to support signal comparability between serial and parallel channel signals in an optical transport network.
2. Description of the Related Art
ITU-T (International Telecommunications Union-Telecommunication) G.693 defines NRZ 10G and 40G optical signal specifications for communication between offices in a maximally 20 km radius. In particular, G.693 defines VSR2000-3R2 which is one of NRZ 40G optical signal specifications having a transmission distance of 2 km using a wavelength of 1550 nm. A 40G 300 pin Multi Source Agreement (MSA) optical module is used as a NRZ 40G serial optical module that satisfies a VSR2000-3R2 specification.
The 40G 300 pin MSA optical module defined in 40G 300 pin MSA uses SerDes Framer Interface (SFI)-5.1 as an OIF standard for connection to a framer or a Forward Error Correction (FEC) processor. The OIF SFI-5.1 defines a deskew channel for compensating for skews between 16 2.5G-level data signals, as well as compensating for the 16 2.5G-level data signals.
Meanwhile, the IEEE 802.3ba standard introduces a Multi-Lane Distribution (MLD) method to a Physical Coding Sub-layer (PCS) so that a 40G Ethernet signal can be all transmitted through four, two or one physical lane, and also defines 40GBASE-LR4 PMD as a physical standard for transmitting 40G Ethernet signals. The 40GBASE-LR4 PMD uses, instead of transmitting a 40G Ethernet signal as a single serial optical signal, a method of assigning different Coarse Wavelength Division Multiplexing (CWDM) wavelengths to four 10G lanes and performing WDM.
As described above, the 40GBASE-LR4 PMD has an optical signal specification that is different from the VSR2000-3R2. In order to satisfy the 40GBASE-LR4 PMD optical specification, since a pluggable type of optical module whose specification is different from the VSR2000-3R2 is required due to the characteristics of the Ethernet, a 40G CFP optical module or a 40G Ethernet QSFP+ optical module that are different from the conventional 40G 300 pin MSA optical module have been released.
However, in order for the 40G-level optical module to have price competitiveness and a large supply, like a 10G-level XFP optical module, it is important to standardize an optical module that can be used in all the 10G Ethernet, 10G SDH, and 10G OTN. Accordingly, the IEEE 802.3 configures an IEEE 802.3bg Task force to complete standardization of 40GBASE-FR PMD that is compatible with the VSR2000-3R2 being a NRZ serial 40G standard that was the existing optical signal specification for 40G SDH and 40G OTN.
An initially developed 40GBASE-FR PMD is expected to support comparability with the existing 40G 300 pin MSA optical module. Accordingly, equipment vendors use a 40G 300 pin MSA optical module to receive all 40G SDH, 40G OTN, and 40G Ethernet signals. However, with the progression of technology, a pluggable type of 40BASE-FR PMD optical module having a size smaller than a fixed type of 40G 300 pin MSA optical module and low power consumption is expected to be released in near future. Since the 40G Ethernet can connect optical modules to each other through four electrical signals using a PCS lane distribution method, it is not preferable to use a SFI-5.1 interface that increases power consumption and has a large volume, and it is efficient to configure an optical module with a 4:1 multiplexer and a 1:4 demultiplexer.